The present invention relates to latex particles with structural units of 2-(methacryloyloxy)ethyl phosphonic acid and composites comprising the latex particles adsorbed onto pigment particles.
Stable aqueous dispersions of polymers containing structural units phophoethyl methacrylate (PEM) are known to improve hiding and stain resistance in paint formulations. The use of PEM-containing paint formulations is well known. For example, U.S. Pat. No. 8,158,713 B1 discloses surprising improvements in stain and scrub resistance for paint formulations containing binders comprising copolymers of ethyl acrylate and relatively low levels of PEM and acetoacetoxyethyl methacrylate. U.S. Pat. No. 5,385,960 discloses an improvement in hiding in paint formulations that include a dispersion of PEM-containing latex polymers adsorbed onto TiO2. U.S. Pat. No. 7,081,488 B1 discloses an increase in hiding efficiency obtained with composite particles having adsorbed PEM-containing polymer particles when the polymer is prepared under conditions of low pH.
Unfortunately, PEM is not commercially available in high purity; although attempts to purify PEM have been described (see U.S. Pat. No. 6,710,161 B1), such processes are not considered to be commercially viable. Thus, PEM is supplied as an impure monomer that contains appreciable amounts of a dimethacryl diester of PEM as well as phosphoric acid, each of which contribute to problems associated with its use. Phosphoric acid, for example, contributes to the hydrolytic instability of the PEM; moreover, the presence of this mineral acid impurity necessitates a much larger charge of neutralizing agent to achieve the targeted pH. The presence of the diester, while not causing adverse effects in the synthesis of the latex, can act as a crosslinker, which can limit the utility of the monomer in applications requiring low molecular weights or solubilization of the emulsion or both. Accordingly, it would be useful to find a phosphorus-containing monomer that has the benefits of PEM and that can easily be prepared with high purity at relatively low cost.